Oxalic acid

Summary

Produced in substantial amounts as by-product of the alumina industry, oxalic acid could be manufactured by alternate means and could also be used in the production of paper pulp.

Oxalic is a simple organic acid used for metal treatment, removing calcium in water, in textiles activities, wood pulp bleaching and for mineral processing. It is now most commonly produced by the oxidation of waste cellulose materials with nitric acid. With shifting economics, it is no longer commercially manufactured in the USA, and China has become the dominant low cost manufacturer.

Oxalic acid does not have a market in Western Australia but it is produced in large quantities as a by-product from processing bauxite. It has application in wood pulp bleaching and required for the production of cerium concentrates (by Ashton Mining, though the required quantities have been reduced to one-tenth to just 550 tonnes).

About 30 000 tonnes of crude sodium oxalate is produced by Alcoa's Western Australia's alumina operations per year and disposed or destroyed. Combined with Worsley Alumina, this represents the destruction of some 27 000 tonnes of oxalic acid that has already attracted the interest of two companies.

It is presently cheaper for the alumina producers to burn and recover the sodium hydroxide than to recover oxalic acid (as say calcium oxalate). For the alumina producers, oxalate represents a loss of caustic soda that is recovered by either burning off the acid, or in the case of Alcoa's Kwinana plant (producing some 6 000 tonnes of oxalic acid), by the more expensive process of treating the oxalate waste with lime. Sodium oxalate could be supplied by Alcoa for the value of caustic soda less the costs of its recovery - ie. the cost of burning or from their Kwinana plant by treatment with lime.

Outlook

Applications for oxalic acid are presently limited. The world price of oxalic acid has declined from about A$1600 to A$600 and Ashton Mining's development of rare earth minerals from Mt Weld, which would require about 550 tonnes of oxalic acid per year (initially 5 000 tonnes), has been deferred.

The substantial volume of oxalic produced by the alumina industry suggests its potential should be carefully considered. For example, it is worth noting that oxalic acid has been used in paper pulp bleaching - an application for this acid that could be evaluated given a proposed paper pulp mill (managed by Bunnings) in the south west of Western Australia. Though it is proposed to use hydrogen peroxide as the bleach, oxalic acid could be considered as an alternative or as a complementing bleaching agent.

Though oxalic is competitively produced in China from waste cellulose, it would not preclude its manufacture in Western Australia with its extensive agricultural base and as a producer of nitric acid. Waste cellulose is also common to the manufacture of carboxymethyl cellulose and furan .